1. Field of the Invention
The present invention is directed to golf balls comprising a core and a cover, wherein the core includes a layer made from a relatively low modulus composition and a layer made from a relatively high modulus composition. Preferably, the core layers are made of a rubber composition comprising cylcoalkene (polyalkenamer) rubber and more preferably polyoctenamer rubber. In one embodiment, the golf ball contains a dual-core, wherein the inner core layer is made of a low modulus polyalkenamer rubber and the outer core layer is made of a high modulus polyalkenamer rubber. In a second embodiment, the inner core layer is made of a high modulus polyalkenamer rubber and the outer core layer is made of a low modulus polyalkenamer rubber.
2. Brief Review of the Related Art
Multi-piece solid golf balls comprising different materials are popular today for several reasons including new manufacturing techniques; availability and cost of raw materials; and playing performance properties. For example, three-piece solid golf balls having an inner core, intermediate layer (inner cover), and outer cover can be made. Typically, the inner core is made of natural or synthetic rubbers such as polybutadiene, polyisoprene, styrene-butadiene, or highly neutralized acid copolymers. Often, the intermediate layer is made of an olefin-based ionomer resin that imparts some hardness to the ball. These ionomer acid copolymers contain inter-chain ionic bonding and are generally made of an α-olefin such as ethylene and a vinyl comonomer having an acid group such as methacrylic, acrylic acid, or maleic acid. Metal ions such as sodium, lithium, zinc, and magnesium are used to neutralize the acid groups in the copolymer. Ionomer resins are available in various grades and identified based on the type of base resin, molecular weight, and type of metal ion, amount of acid, degree of neutralization, additives, and other properties. Finally, the outer cover of conventional golf balls is made from a variety of materials including ionomers, polyamides, polyesters, polyurethanes, and polyureas.
Manufacturers consider various properties when designing and developing golf balls for recreational and professional golfers. The flexural modulus of materials used to make golf balls is an important property. The resiliency and rebounding performance of the golf ball are based primarily on the core of the ball. The core acts as the engine for the ball. Hard materials having a relatively high flexural modulus can be used to make a harder core. The harder core helps impart a higher initial velocity to the golf ball so it travels a greater distance. This is particularly desirable for driver shots off the tee. However, one disadvantage with these harder balls is they tend to provide the player with a rougher and harder “feel.” The player may experience a more unnatural feeling when he/she strikes the ball with the club face. Moreover, the player tends to have less control when hitting relatively hard balls. It is more difficult to hit such hard balls with the proper touch and spin. This is particularly troublesome when making approach shots with irons.
The golf ball industry is constantly looking to develop compositions that can be used to make multi-piece golf balls having good distance and playability. For example, Kim et al., U.S. Pat. No. 7,528,196 and U.S. Patent Application Publication US 2009/0191981 disclose a golf ball comprising a core, cover layer, and optionally one or more inner cover layers, wherein at least one portion of the ball comprises a blend of a polyalkenamer and polyamide. The polyalkenamer/polyamide composition contains about 2 to about 90 weight % of a polyalkenamer polymer and about 10 to about 98 weight % of a polyamide. The '196 patent and '981 Published Application further disclose that the polyalkenamer/polyamide composition may be blended with other polymers including polybutadiene, polyisoprene, polychloroprene, polybutylene, and styrene-butadiene rubber prior to molding. However, neither the '196 patent nor '981 Published Application discloses a golf ball containing at least one layer made from a relatively low modulus polyalkenamer rubber composition and at least one layer made from a relatively high modulus polyalkenamer.
In Voorheis et al., U.S. Pat. No. 6,767,940, a golf ball having a core, an intermediate layer, and a cover is disclosed. The core is formed from a composition containing an elastomeric polymer, free-radical initiator, and at least one stable free-radical. The stable free-radical increases the scorch time (time between start of reaction and onset of cross-linking) of the elastomeric polymer. The '940 patent discloses numerous materials that can be used to form the intermediate layer, which is distinguishable from the core, including natural rubbers; balata; gutta-percha; cis-polybutadienes; trans-polybutadienes; synthetic polyisoprenes; polyoctenamers; polypropylene resins; ionomer resins; polyamides; polyesters; urethanes; polyureas; chlorinated polyethylenes; polysulfide rubbers; and fluorocarbons.
In Sullivan et al., U.S. Pat. Nos. 6,783,468, 7041,009, 7,044,864, 7,118,495, and 7,125,345, a golf ball having a low compression and high coefficient of restitution (COR) layer supported and reinforced by a low deformation layer is disclosed. The preferred polymeric composition for the high COR layer is a base rubber compound, a co-reaction agent, a halogenated organosulfur compound, and a co-cross-linking or initiator agent. The low deformation layer may be made of rigid plastics or polymers reinforced with high strength organic or inorganic fillers or fibers. In one embodiment, the golf ball comprises an innermost core, an outer core, and a cover. The inner core comprises a low deformation material and the outer core comprises a rubber composition. The patents disclose that natural rubbers, including cis-polyisoprene, trans-polyisoprene or balata, synthetic rubbers including 1,2-polybutadiene, cis-polybutadiene, trans-polybutadiene, polychloroprene, poly(norbornene), polyoctenamer and polypentenamer may be used for the outer core. However, there is no disclosure of golf balls containing at least one layer made from a relatively low modulus polyalkenamer rubber composition and at least one layer made from a relatively high modulus polyalkenamer.
In addition, Llort, U.S. Pat. No. 4,792,141 describes a balata-covered golf ball, where up to 40% of the balata used to faun the cover has been replaced with polyoctenylene rubber. The golf ball contains a core and a cover wherein the cover is formed from a composition comprising about 97 to about 60 parts balata and about 3 to about 40 parts by weight polyoctenylene rubber based on 100 parts by weight polymer in the composition. The '141 patent discloses that using more than about 40 parts by weight of polyoctenylene produces deleterious effects.
One objective of the present invention is to develop compositions that can be used to make a core for a golf ball, wherein the core provides the ball with high resiliency along with a comfortable and soft feel. The present invention provides golf ball core compositions having such properties as well as other advantageous characteristics, features, and benefits.